EventSub has no bulk create. But you can create multiple topics where transport
No you do not need 1 websocket per topic, you can subscribe to as many as you can fit within the posted limits.
This example - https://barrycarlyon.github.io/twitch_misc/eventsub/websockets/web/basic/ creates 1 websocket and adds 6 subscriptions to it.
“Regular chat” messages are not provided as an eventsub topic.
But things like cheer and resubscriptions will provide the message text attached to that event.